Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
In order for the middle or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle or large-sized battery module to be configured to have a structure in which a plurality of battery cells is electrically connected in series to each other, and the battery cells are stable against external force.
Also, battery cells constituting such a middle or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. If heat, generated from unit cells during the charge and discharge of the unit cells, is not effectively removed from the battery module, the heat accumulates in the battery module with the result that deterioration of the unit cells is accelerated. According to circumstances, the battery module may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
Meanwhile, in a case in which a battery module or a battery pack including plate-shaped battery cells, each of which has an electrode assembly of a cathode/separator/anode structure mounted in a battery case formed of a laminate sheet including a resin layer and a metal layer, is used as a battery for vehicles, such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and electric vehicles (EV), it is necessary to guarantee long lifespan of the battery cells. To this end, a cooling system to maintain the battery cells at a specific temperature or less is provided. Also, it is necessary to maintain temperature deviation between the battery cells at a specific range or less, thereby reducing deterioration deviation between the battery cells and thus preventing abrupt lowering in performance of the battery pack.
In a cooling mode using a gas, such as air, a cooling channel is lengthened, and therefore, the temperature of the air is increased during cooling, resulting in great temperature difference between the battery cell located at the front part of the battery pack and the battery cell located at the rear part of the battery pack. In particular, recently, various shapes of battery packs have been required based on installation conditions of an external device. For a battery pack configured by stacking two or more battery modules, the temperature difference between battery cells is greatly increased if the same cooling channel as in the conventional battery pack is used.
Also, in a case in which the battery cells are stacked along the cooling channel, air introduced into the battery pack gradually rises while cooling the surfaces of the battery cells as the length of the cooling channel is increased, resulting in great temperature difference between the battery cell located at the front part of the battery pack and the battery cell located at the rear part of the battery pack. That is, the internal resistance deviation between the battery cells and the deterioration deviation between the battery cells are caused due to the temperature difference between the battery cells with the result that overall performance of the battery pack is greatly affected. Also, overall performance of the battery pack is dependent upon the performance of the most deteriorated battery cell.
Consequently, there is a high necessity for a battery pack configured to have a specific structure using a cooling system that is capable of achieving uniform flow of a fluid and reducing temperature deviation as needed.
Such temperature control is necessary not only for a cooling system which removes heat but also for a heating system which supplies heat to solve overcooling.